Remeasurement of capture to positron decay ratios in22Na and65Zn and comparison with theory

In the decay of²²Na theEC/β ⁺ ratio for theβ-transition to the 1275 keV-level was measured to beEC/β ⁺=0.1050 (29). Single and coincidence counting was performed using a 16% Ge(Li) and an NaI well-type detector. For⁶⁵Zn theK/β ⁺ ratio for the ground state transitionK ₁/β ⁺=30.3 (10) was obtained using the same apparatus and in addition a 10 mm diam. × 5.4 mm Si(Li) detector. The results are compared with earlier experiments and with theory.     

The alpha-branching ratios of the188,190,192Pb isotopes

Theα-branching ratios (b _α ) of^192,190,188Pb are measured using mass-separated sources. Different experimental set-ups are used — one detector as well as two detector set-ups — thereby detecting theα particles from the parent and/or viaα decay formed daughter nuclei, theβ-delayed gamma radiation from the parent and/or viaβ decay formed daughter nuclei and the Tl KX rays from electron capture decay. Values forb _α of 6.2(6) 10^?5 and 4.0(4) 10^-3 were found for^192,190Pb respectively. For¹⁸⁸Pb, limits on theb _α values were obtained: 0.03<b _α <0.10. A careful analysis of the previously reportedb _α values showed that the discrepancies in theb _α values were not due to inadequate correction procedures, as was suggested, but to experimental uncertainties in the efficiency determination of the different detection set-ups and to an unreliableβ-decay scheme for¹⁸⁸Pb. Theb _α obtained in this work show that the leadα decay is not faster than the Hgα decay and that there is no need to assume a disappearance of theZ=82 shell closure halfway betweenN=82 andN=126.     

The mass of the nucleus148Dy

Usingγγ coincidences theEC(K)/β ⁺ ratio for theβ decay¹⁴⁸Dy→¹⁴⁸Tb has been determined.¹⁴⁸Dy has been produced through the irradiation of⁹³Nb with 249 MeV⁵⁸Ni ions. The mass of¹⁴⁸Dy has been deduced. With the help of knownQα values the masses of¹⁵²Er,¹⁵⁶Yb,¹⁶⁰Hf and¹⁶⁴W have been obtained. The experimental masses are compared with different current mass formulae.     

GoldL-shell ionization probability by 1 MeV proton at large scattering angles

The impact parameter dependence of the ionization of GoldL-subshells has been measured and compared to theoretical values calculated in the SCA framework by Aashamar et al. [17]. Special attention has been paid to large scattering angle measurements and results are obtained for0 _lab=30°, 45°, 65°, 90°, 110°, 130°, 153° and 166°. Taking into account the sum ofL _α ,L _β ,L _γ ,L _α ,L _l lines we conclude firstly that the experimental ionization probabilityP(b) is in good agreement with the theoretical values. Secondly, comparing experimental and theoretical intensity of (L _α +L _l ) and (L _γ +L _β ) X-ray lines, we show that ionization ofL _II andL _III subshells is also fairly well described by the SCA model.     

Search for an isomer in94Rb

Measurements of theβ-ray half-life,γ-ray and X-ray spectra andγ-ray half-lives have been done with a plastic scintillation detector, a high resolution Ge(HP) detector and a 142 cm³ Ge(Li) detector to search for an isomeric state in⁹⁴Rb. Mass-separated activities of⁹⁴Rb were obtained from the He-jet type on-line mass-separator at the Kyoto University reactor. No isomeric transition was found in theγ-ray and X-ray measurements with the upper limits of 3×10^?4 and 8×10^?5, respectively, as compared with the 836.9 keV transition. Half-lives obtained from theγ-ray decay measurements are discussed in the light of classification given byQ _β -value measurements.     

Shifts of X-ray characteristic L lines of free atoms of rare-earth metals

Results of the study of X-ray characteristic spectra of free atoms of a number of rare-earth metals from Ce to Ho are reported. L _α1 and L _β1 lines were studied, and the shifts of the peaks of emission lines of free atoms relative to their positions in the case of emission by the solid aggregate state were measured. The data obtained enable one to use the corresponding X-ray characteristic lines as references with the accuracy Δλ/λ≈10^?5. The Z-dependences of shifts are plotted.     

Gamma-ray-L-x-ray directional correlations in182W

Directional correlations between gamma radiation andL x-rays in¹⁸²W have been measured. The x-rays are emitted following the internal conversion process of the 100.1 keV 2⁺ → 0⁺ transition. The experimental results for anisotropies involving gamma radiation emitted in the 1189.0 keV transition andL x-rays are A(γ?L _l )=?0.073(27),A(γ?L _α)=?0.0102(45),A(γ?L _β)=?0.0031(35), andA(γ?L _γ)=?0.007(13). The value deduced for the coefficientU ₂(e) pertaining to the converted transition isU ₂(e)=0.52(8) in reasonable agreement with the theoretically expected value 0.410. A note is given on the use of internal conversion radial matrix elements.     

Internal conversion coefficients and penetration effect for the 279 keV transition in203Tl

The internal conversion process of theM1+E 2 mixed 279 keVγ-ray transition in the decay of²⁰³Hg has been reinvestigated. The emission rate of theK-shell internal conversion electrons was determined with an electron X-ray coincidence measurement using a magneticΒ-spectrometer and a Si(Li) detector of high energy resolution. Conversion electron ratios were obtained from electron spectra recorded as a function of momentum. The disintegration rate has been taken from measurements with a calibrated NaI(Tl)γ-ray spectrometer. Following results have been deduced: α=0.2279±0.0024, α _K =0.1653±0.0017, α _L =0.0475±0.0013,K/(L+M+?)=2.64±0.03,K/L=3.48±0.12,L/(M+N+ ?)=3.14±0.12. On the basis of the experimental results on theK-shell internal conversion coefficient,α _k , and the conversion ratioK/(L+M+?) the penetration effect on the internal conversion of theM1 part and the mixing ratio,δ ², of the 279 keVγ-ray transition in²⁰³Tl have been studied. Calculations were made using Hager and Seltzer's formalism and their theoretical internal conversion coefficients. The results are consistent with a mixing ratio ofδ ²=1.32±0.11 and a penetration parameter ofλ=6.8 ±0.8.     

Determination of the K-shell internal conversion coefficient for the 37.2 keV transition in the decay of121mSn

TheK-shell internal conversion coefficientα _K for the 37.2 keV transition (7/2⁺→5/2⁺) occuring in¹²¹Sb afterβ ^? decay of¹²¹ mSn has been redetermined applying theX- toγ-peak method (XPG). Measurements of photon spectra from thin sources have been performed at various source-detector distances with a high resolution, efficiency calibrated Si(Li) detector. Values ofα _K have been deduced from the number of emittedKX rays compared to that of the emittedγ rays. TheK-shell fluorescence yield for antimony has been taken from the literature. From in total 14 experimental runs a mean result ofα _K =9.52±0.27 has been obtained. The quoted uncertainty comprising statistical and systematic parts is discussed in detail. The present result is compared with the few existing earlier experimental values and with the theoretical value interpolated from the most recent tabulations.     

New screening doublets in x-ray satellite spectra

Recent scrutiny of the relevant data available at present on x-ray satellite spectra in theK, L andM regions revealed the existence of two new satellite pairsα″α′ andα″α′ ₃ ′ in theKα satellite group, three pairsα′ ₂ α″,α′ ₂ α^VI andα? α ^IV in theLα satellite group, twoLβ ₂ satellite groups; viz.,β ₂ ^(b) (β ₂ ^I ,β ₂ ^II β ₂ ^(c) ) andβ ₂ ^(c) (β ₂ ^I β ₂ ^II ), two pairsγ′₁ γ′₂ andγ′₁ γ′_2′ in theLγ satellite group and also a pairβ _II β _III in theMβ satellites, which are all found to be governed by the screening doublet relationship,Δ(v/R)^1/2=constant.     

Angular Dependence of L X-ray Relative Intensities of Uranium and Thorium at 59.5 keV

INTRODUCTION

The knowledge of relative intensities of K, L and higher shell X-rays is needed for the investigation of various phenomena in atomic physics. In earlier studies, L X-ray relative intensities and energies have been reported for many elements by several investigators [1–5], but the angular dependence of L X-ray relative intensity has not been reported. According to Flugge et a1 [6], if the angular momentum J=1/2 and J>1/2 of the originating shell, then the angular distribution of X-rays is isotropic and anisotropic, respectively. From this idea, L_α, L_l and some of L_β, intensities are dependent on changing the scattering angles. In this study, we have measured the angular dependence of L_α, La_l, L_α/L_β, and L_α/L_γ, intensity ratios of U and Th at different angles varying from 45° to 135°.     

In-beam study of127Xe

The level structure of the¹²⁷Xe nucleus has been studied through the¹²⁵Te(α, 2n)¹²⁷Xe reaction atE _α=27 MeV by in-beamγ-ray spectroscopic methods including three-parameterγ-γ-t coincidences, angular distribution and linear polarization as well as lifetime measurements. The results supplemented current information and, in particular, established the existence of a new isomeric state having a half-life of 25±3 ns.     

A note on60Co decay

Theγ-rays from⁶⁰Co have been studied with a 30 cm³ Ge(Li) detector. Gamma rays of energies 826.4 and 2,158.9 keV which are expected on the basis of the⁶⁰Co decay scheme were sought but not observed. Their intensities are <0.02% and <0.002%, respectively, of the⁶⁰Co disintegrations. Any direct feeding from the (5⁺)⁶⁰Co ground state to the (2⁺) 2,159 keV level is <0.022%, yielding a logft>12.3 for the 664 keV second-forbidden uniqueβ-transition. Radioactivity⁶⁰Co; measuredE _γ,I _γ.⁶⁰Ni deduced levels, logft. Ge(Li) detector.     

Search for neutrino radiative decay with a prototype Borexino detector

Results of background measurements with a prototype of the Borexino detector were used to obtain bounds on the lifetime of radiative neutrino decay ν_H→ν_L+γ. The new lower limit for the lifetime of pp and ⁷Be neutrinos is τ_c.m.(ν_H→ν_L+γ) /mν≥4.2×10³ s eV^?1(α)= 0). It is more than an order of magnitude stronger than the value obtained in previous experiments using nuclear reactors and accelerators.     

The decay of115 mIn

The decay of^115m In has been investigated using accurate counting methods. The emission rate of conversion electrons plusβ ^?-particles was determined with a 4π proportional flow counter. The total andK-shell internal conversion coefficients of the 336 keVγ-ray in¹¹⁵In were measured by the electron X-ray coincidence method using combinations of a Si surface barrier with a NaI(Tl) detector and of a magneticβ-spectrometer with a high energy resolution Si(Li) detector, respectively. The conversion ratioR=K/(L+M+...) was deduced from electron spectra recorded with the magneticβ-spectrometer. The 336 keVγ-ray emission rate of all used sources was determined with a calibrated NaI(Tl)γ-ray spectrometer. A Ge(Li) detector has been used to determine the relative intensity of the 497 keVγ-ray in¹¹⁵Sn. As results have been deduced the 336 keVγ-ray emission per decay (N _γ1/N ₀=(45.9 ± 0.1)%), the total internal conversion coefficient (α=1.073 ± 0.014), theK-shell internal conversion coefficient (α _K=0.843±0.012), the conversion ratioR=3.63±0.07, theβ ^?-transition per decay going to the ground state (N _β1/N ₀=(5.0 ± 0.7)%) and to the first excited level in¹¹⁵Sn¹¹⁵Sn(N _β2/N ₀=(0.047 ± 0.002)%), and the 497 keVγ-ray emission (N _γ2/N _γ1=(0.103 ± 0.004)%). From the obtained internal conversion data it follows that the 336 keVγ-ray transition is ofM4 character with anE5 admixture of less than (3.5±1.5)%. The half-life of the isomeric state¹¹⁵ mIn has been determined with four different methods. The result isT _1/2=(4.486±0.004) h.     

Gamow-Teller strength in the β+ decay of104In

Theβ-strength function of¹⁰⁴Cd is studied in theβ ⁺/EC decay of mass-separated¹⁰⁴In. The determination of theβ ⁺ feeding and theβ ⁺/β ⁺EC ratio is the result of the simultaneous measurement of beta and gamma rays in one semiconductor beta-spectrometer. Information on the strength function near theQ _EC value is obtained from the detection of high-energyγ rays. The total observedβ strength amounts up to 10% of the Extreme Single-Particle Shell Model value. A strong enhancement in theβ ⁺/EC feeding to a group of levels around 5.6 MeV shows the influence of the Gamow-Teller Resonance.     

Investigation of the e<Subscript>0</Subscript>-electron yield from the surface of thin films under bombardment by α and β particles from radioactive sources

The yields of near-zero (e₀) electrons from the surface of targets with different Z under their bombardment by α particles from ²²⁶Ra decay were measured by the method of e_α coincidences. The ratios of the e₀-electron yields for α particles with different energies E _α are described well by the dependence Y _e (E _α) ～ υ _α ^?1 , where υ _α is the α-particle velocity. The e₀-electron yield from the surface of thin films under their bombardment by β particles from radioactive sources with ¹⁵²Eu, ¹⁵⁴Eu, and ²²⁶Ra has been investigated by the method of eγ coincidences. It is established that ionization rate of target atoms in this case is inversely proportional to the velocity of incident β particles (υ _β ^?1 ), i.e., is proportional to the time of atomic electron perturbation induced by a β particle passing near an atom.     

Ground state bands in142Gd and140Sm

The ground state bands of theN=78 isotones¹⁴² Gd and¹⁴⁰Sm were observed up to the 8⁺ state by bombarding¹⁴⁴Sm and¹⁴²Nd withα-particles of energies between 80 and 130 MeV. Excitation functions,γ-γ coincidences, lifetimes and angular distributions were measured. The ground state band in¹⁴⁰Sm is partially fed by an isomeric state ofT _1/2?17ns. No such isomerism is observed for¹⁴²Gd. The level energies are very similar in both cases and agree well with the predictions of the VMI model.     

Determination of fission barrier heights from β-delayed fission

Beta delayed fission (βDF) gives a possibility to investigate the fission barrier for nuclei far off beta stability. However, before any information on the fission barrier can be extracted, the effect of low-lying structures in the beta-strength function (S _β) on theβDF branching ratio has to be considered. This is in general not done. In this paper the lowlying structures that occur inS _β are discussed and microscopic calculations for the Gamow-Teller strength function are presented for²³²Th (β ^?-decay) and²³²Pu,²⁴⁰Cm,^244,248Cf and²⁴⁸Fm (β ⁺-decay). Using the calculated strength functionsβ ⁺DF branching ratios are calculated and compared with the experimental ones. The sensitivity of the results to different shapes ofS _β is investigated. It is concluded that, when the expected structures inS _β are considered, there are at present no indications fromβ ⁺ DF measurements that the errors in the fission barrier calculations are larger than the uncertainty given for those calculations. The difference in magnitude between theβ ^? DF and theβ ⁺DF branching ratios is also explained by the occurrence of low-lying structures inS _β.